Well, being a werewolf is fairly casual. A part-time monster, if you will. If you behave yourself, watch where you transform and suppress your primal instincts, you'll get alone swimmingly with the people of Skyrim. No one will ever be the wiser. The only penalty is you no longer get the rested bonus when you sleep. That's not a huge deal.
Vampirisim is a full time job! You're always a vampire, even when you're not in Vampire Lord form. Sunlight will always affect you, you will always need to feed, you will always be weak to fire, you will always be outed if you get to close to NPCs like The Vigilants of Stendarr.
For this reason I chose Vampirisim. I find it more immersive; more of a total experience. Even after they took away some of its teeth (So to speak!) with Dawnguard by removing hostility towards a stage 4 vampire. I rarely, if ever, use the Vampire Lord form. Though I did max its perks for the sake of doing it. I just enjoy the little things that being a vampire brings to the game, both the strengths and weaknesses.